The two-dimensional traffic model of Biham, Middleton and Levine (Phys. Rev. A, 1992) is a simple cellular automaton that exhibits a wide range of complex behavior. It consists of both northbound and eastbound cars traveling on a rectangular array of cells, each cell equipped with a traffic signal. The traffic signals switch synchronously from allowing northbound flow to eastbound flow. By gating individual traffic signals, i.e. allowing individual traffic signals to break from synchrony in predetermined, deterministic scenarios based on the local state of traffic, the range for which the system self-organizes into a state of unimpeded flow is extended. On a 100x100 cell array, this additional intelligence enables accomodation of 200 cars more than the original BML model, without any reduction in average velocity.
Danforth, Christopher and Brown, Daniel, "Intelligent Traffic Signals: Extending the Range of Self-Organization in the BML Model" (2013). University of Vermont Transportation Research Center. 213.